(1) Field of the Invention
The present invention relates to a storage container for precision substrates which is used for storage, preservation, in-process work, transportation of precision substrates such as aluminum discs, semiconductor wafers, mask glass substrates, etc., and more specifically relates to improvement of the container body, door and locking mechanism of a storage container for precision substrates which can be connected to a system having a standardized mechanical interface used in the semiconductor wafer fabrication process.
(2) Description of the Prior Art
A conventional storage container for precision substrates, though it is not illustrated, includes: a pod for accommodating multiple semiconductor wafers (to be referred to merely as wafers) etc., in alignment; a hollow door element for hermetically closing the open front of the pod; and a locking means for keeping the closed state when the door has been closed.
The locking means is categorized into two types, the inner lock type and the outer lock type. An inner lock type locking means is configured of multiple clamp bores formed in a depressed manner on the upper and lower inner peripheral surfaces of the open front of the pod, multiple passage openings pierced, correspondingly to the multiple clamp bores, on the upper and lower peripheral surface of the door element, a rotary cam which is axially supported in the center inside the door element and is rotated from an external access, and a pair of latch plates disposed above and below and each having a guide groove to be engaged with some play with a corresponding coupling pin on the rotary cam surface at the periphery thereof. Each latch plate is made of metal so that it can provide high rigidity and has an engagement claw disposed in the distal end to be projected through the passage opening for engagement with the corresponding clamp bore.
Compared to this, an outer lock type locking means is configured of multiple engaging pieces pivotally formed in the outer peripheral portion of the open front of the pod and multiple projections formed on the peripheral surface of the door element. These multiple engaging pieces and projections function so as to engage each other when the door element is closed.
In the above configuration, when wafers need to be stored, preserved, transported, multiple wafers are loaded one by one into the pod first and then the door element is fitted hermetically to the open front of the pod. Thereafter, the door opening/closing device of an unillustrated processing machine rotates the rotary cam in one locking direction so that each latch plate moves linearly and projects outwardly from the inner position inside the door element and hence engagement claws become engaged with the clamp bores to maintain the locked state of the door element.
When the wafers which have been stored, preserved, transported etc., need to be processed, the door opening/closing device of the processing machine rotates the rotary cam in the other direction to unlock, so that each latch plate moves linearly and returns inwardly from the outer position inside the door element and hence engagement claws become disengaged from the clamp bores thus permitting the door element to be released. When the door element thus becomes openable, the door element is removed from the pod by vacuum suctioning or other ways. Then the wafers are taken out one by one from the lowermost one so that the wafers will be processed in the predetermined manner.
Prior art disclosures related to the technique of this kind are also found in Japanese Patent Application Laid Open Hei 9 No.88398 and Hei 8 No.340043, Japanese Patent Application Disclosure Hei 4 No.505234 and Hei 7 No.504536.
Thus, the conventional storage containers for precision substrates have been thus configured so that the door element may be merely fitted in the open front of the pod and may be merely taken off, without taking into consideration the looseness of the door element due to repeated usage. Further, no consideration has been given for the displacement of the door element from the pod due to errors of repeatability etc. of the operation of the processing machine for retaining the door element when the door element is taken out. If the door element works loose or is fitted out of position, each clamp bore, passage opening and engagement claw are positioned out of line when the door element is fitted, making it difficult to lock the door element or causing abrasion between the pod's open front and the door element's edge which will produce contaminants such as floating particles etc.
In recent years, in order to realize a higher packing density configuration, a finer structure and an improved production efficiency of semiconductor integrated circuits, an agreement on the standardization of large-sized wafers (of 300 mm in diameter) has been reached and intensive research and development have been in progress. However, for example, if the pod is simply made greater in order to store 300 mm wafers, the problems as follows will occur. First, if the pod is made greater, there is a risk that the latch plates may warp during locking and hence the fully open front of the pod cannot be uniformly sealed in a well enough manner. Further, conventionally, the latch plates have been made of metals, however, this has been the hindrance to rinsing of the door element, giving rise to a serious problem of the wafers being contaminated.